The Map Apps That Move You in the Right Direction - NYTimes.com

But frustrations remain. Apple Maps still lacks public transit directions — it offers just driving and walking navigation. There is, however, a new option called Apps. If you select that option, Apple Maps can open up a second transportation app that you have installed, like a subway app, Google Maps or MapQuest, that does have transit information. The second app opens when you tap a Route button.

But that extra step seems unnecessary. It’s a hack, not an actual fix for the missing transit maps."